The present invention relates generally to image transfer devices and, more particularly, to techniques for calibrating such devices and for locating a document therewithin.
Image transfer devices, such as scanners, copiers, photocopiers and the like are in virtually universal use. They provide efficient and effective techniques for transferring images from one medium to another. It is important in most cases that the copy accurately represent the original.
With accurate copying as a goal, the design and manufacture of image transfer devices present a myriad of challenges ranging across a broad spectrum of engineering disciplines. For example, a suitable optical system, under microprocessor control, must be controlled to move in a housing having many moving parts. In typical cases, the device is used by an operator who knows and cares little about machine function and is interested only in the end result. Complicating the situation is the fact that differing sizes of documents, legal, A4 and letter size paper, for example, may be involved and these may be in color. For these reasons, expensive firmware algorithms are required for controlling system operations in some conventional scanners.
A challenge for the image transfer device manufacturer is to make a product capable of effective operation in a variety of environments, faithfully reproducing a variety of media, in black and white and color, while substantially reducing the necessity of input from the operator. Attempts to meet this challenge often result in an increase in firmware algorithmic controls, in spite of the desirability of reducing such controls to achieve a simpler and less expensive system.
For reasons of convenience, the following description will relate to scanners but it will be recognized by those skilled in the art that the principles herein apply as well to other image transfer devices, such as copiers and the like.
In a conventional scanner, a document to be copied is placed on a glass plate, housed in a bezel, while a scan head moves on a rod along a y axis during the copying operation. In order for a true copy to result, relationships among rod and bezel, and bezel and glass, must be carefully controlled. Conventional image transfer devices sometimes fail to afford appropriate component mechanical alignment and, as a result, copies of poor quality result.
Another important factor in scanner operation relates to calibration of the device. In some cases, this is accomplished immediately prior to an individual scan. In conventional devices, the scanner calibrates from a white ink or white material, in the form of a sticker, attached to the glass plate. Such techniques can result in diminished copy quality or in a need for expensive firmware to compensate for system shortcomings.
For example, in scanners where a white sticker is applied to the glass, placement is critical and, in some prior art devices, difficulty in locating the material in the same location, on a consistent basis, results in diminished scanner performance. In the case of stickers, applied directly to the glass plate, contamination of the critical calibration area is possible. Such contamination is sometimes produced by the ammonia in glass cleaners or by spillage of a beverage on the glass. These factors emphasize the need for a consistent and reliable technique for placement of scanner calibration information while diminishing the likelihood of environmental contamination.
Other problems are experienced in conventional scanners which calibrate from white ink applied directly to the glass surface. In such cases, variations in ink thickness result in changes in reflected white color intensity as seen by the scanner CCD during calibration. For example, a relatively thin area of ink presents a gray background to the CCD. In addition, scratches or imperfections in the ink can cause related pixels to be incorrectly calibrated, with defects such as streaks produced in the copy. As in the case of the white calibration sticker, environmental contaminants can impair system function. Still another problem is experienced as light piping whereby the ink displays more brightly in the center region of the ink area than at the edges.
Attempts have been made to correct the prior art problems set forth above, and to reduce non-uniform effects from back reflected light that passes through the white ink or the sticker and then reflects back through the calibration area. In some cases, a black label or backing feature is fixed to a plastic scanner bezel housing directly above the white calibration area. The glass plate with the calibration ink or attached white sticker is then loosely housed in the scanner bezel. While this technique may have some limited value, the desired level of calibration precision is still not achieved.
Another conventional solution to calibration problems is the use of silk screening on the glass plate. A limitation of this approach is a tendency for light piping to occur in the calibration area. This adds to system cost since the problem must be compensated for firmware algorithms.
The litany of prior art limitations includes yet another. In conventional scanners, because the glass plate in some cases can not be accurately located to scanner CCD pixel positions, the white calibration area can not be used for anything beside calibration. That is, no features can be integrated into the calibration area to aid in an accurate determination of parameters such as scanner skew, magnification, document reference, or black calibration information.
As a result, since the calibration area can not be dimensionally controlled well enough for accurate placement of locating features, the document origin is located on a plastic piece that is snapped into the scanner bezel. This results, once again, in less than optimal system performance because of a large tolerance stack between the scanner CCD pixel home location and the document home location.
In view of the foregoing, it is apparent that a need exists for a technique that reliably affords improved scanner calibration while substantially reducing or eliminating a need for firmware controls. Desirably, such a technique would be low in cost and easily adapted to the scanner manufacturing process.
The present invention affords a technique for substantially and reliably improving calibration precision while reducing costs. In a presently preferred embodiment, there is provided a device for calibrating a scanner which includes a transparent plate installable in the scanner for supporting a document containing indicia to be transferred, and an elongated calibration label fixed to the plate adjacent to, and parallel with, an edge thereof. The label includes an opaque white substrate having a bottom surface which includes a first zone containing white calibration ink and a second zone containing black calibration ink. The white ink contains machine readable information comprising data for controlling skew, magnification, and document reference while the black ink contains data for controlling black calibration. The top surface of the calibration label includes reference indicia for aiding a user in operating the scanner. The first and second zones are surrounded by an adhesive zone for adhering the label to the plate and for isolating the zones from environmental contaminants. A method is provided for fixing the label to a scanner plate for installation in a scanner bezel.
A presently preferred embodiment of the invention affords several advantages with respect to the prior art. White and black calibration are efficiently and effectively achieved without concern for variations in silkscreen thickness since the ink is applied to an opaque surface. Because ink to printing tolerances are easily and relatively tighter to control, new features can be incorporated into the calibration area of the label. These features may include, for example, scanner skew, magnification, document reference, and black calibration.
Another advantage of the present invention relates to protection of the calibration area from environmental contamination. With fixation of the label to the glass plate, an adhesive moat is formed around the calibration area. This moat prevents color contamination from moisture or damage from liquids such as beverages or ammonia from glass cleaning fluids.
In addition, since the calibration label is adhesively attached to the glass at the adhesive moat, the white and black calibration areas are in direct, but not intimate, contact with the glass surface. This factor allows improved simulation of how a document is viewed. The result is improved scanning precision.
Further, the novel calibration label of the present invention can now be utilized for document placement, so external borders to place a document are no longer required and cosmetic artwork can be located opposite the calibration side of the label to direct the user of the scanner how to place a document.
Finally, enhanced construction of calibration color and calibration placement allow for relaxed manufacturing tolerances and a reduction in total system parts, without any sacrifice in system performance.
In summary, a device embodying the invention is easy to install and mechanically simple. Yet, in contrast to conventional scanners, it substantially increases calibration precision and system operation at reduced cost.